- Haskell-Cafe - Haskell.org

Is the wiki really this out of date?
by Dominic Steinitz 23 Feb '14

23 Feb '14

I just looked at the wiki page for the IRC channel: http://www.haskell.org/haskellwiki/IRC_channel. It’s got some great charts but they last seem to have been updated in 2009. Is that really the case? And does anyone know how to get them up to date. I can see this: http://tunes.org/~nef/logs/haskell/ so I think the chart showing kb of text per day should be easy enough. Not sure about the social graph or the noun chart though. I know I can get number of people on the channel by /names but that only gives a snapshot. Has anyone any idea on how to get historical data on number of names? Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

2 1

ANNOUNCE: Win32-dhcp-server
by Michael Steele 23 Feb '14

23 Feb '14

I'm pleased to announce the first version of Win32-dhcp-server [1]. The purpose of this library is to query and control a Microsoft DHCP server. Enough functionality is defined so so that Ipv4 client lease and reservation records can be manipulated from software. I started this at the 2011 Portland hackathon (HacPDX-II), and have been working on it off and on since then. After adding support for a few more commands last month I realized it was probably ready to publish. Please report any bugs, comments, or feature requests to the github [2] repository. [1]: http://hackage.haskell.org/package/Win32-dhcp-server [2]: https://github.com/mikesteele81/Win32-dhcp-server -- -- Michael Steele

1 0

Hdevtools cabal support
by Maxim Kulkin 22 Feb '14

22 Feb '14

Hi, I'm pretty new to Haskell, but was doing Haskell development for several month. I'm fan of Vim editor and was happy to find out that there are good tools to support Haskell development with Vim, e.g. vim-hdevtools. But it turned out that it not of much use in my project where we rely on Cabal packages and sandboxes. As part of scratching own itch I have implemented support for Cabal packages for Hdevtools. I invite everyone interested to try, review and provide feedback on this. The patch is not yet merged into master branch, so to install it you need to check it out from my repository: git clone https://github.com/maximkulkin/hdevtools.git cd hdevtools git checkout cabal-support cabal install So, to be able to use hdevtools with Cabal, you just need to run hdevtools from inside your Cabal project, e.g. hdevtools check src/MyFile.hs hdevtools info src/MyOtherFile.hs DoThat Hope this will save someone's day. Max

6 15

Problems on installing sizes-types package
by Rodrigo Ribeiro 21 Feb '14

21 Feb '14

Hello to all! I'm trying to install the sized-types package, a dependency for kansas lava: http://hackage.haskell.org/package/sized-types using cabal, and the following error message is returned: Data/Sized/Sparse/Matrix.hs:61:26: Could not deduce (Eq a) arising from a use of `prune' from the context (Size m, Size n, Size m', Size n', n ~ m', Num a) bound by the type signature for mm :: (Size m, Size n, Size m', Size n', n ~ m', Num a) => Matrix (m, n) a -> Matrix (m', n') a -> Matrix (m, n') a at Data/Sized/Sparse/Matrix.hs:50:7-112 Is it a known issue? Is there some way to solve it? I'm using GHC 7.6.3 and plataform 2013.2.0.0. Best, Rodrigo

2 1

Haskell Platform website error
by Omari Norman 21 Feb '14

21 Feb '14

Inaccuracy in Haskell Platform website: it says version 2013.2.0.0 includes containers-0.4.2.1: http://www.haskell.org/platform/changelog.html However the containers included in GHC 7.6.3 and, therefore, with this version of Haskell Platform is in fact version 0.5.0.0. There's no apparent contact link on the website; who should I report this to? Thanks. --Omari

8 10

Haskell Statistics
by Dominic Steinitz 21 Feb '14

21 Feb '14

Hi I am looking for statistics on usage of Haskell, ghc and the Haskell Platform and their growth. Current usage would be great but I’d also like usage by year or month. Useful proxies might be number of people signed up to haskell-cafe and #haskell (also by year or month). The impression I have from the number of jobs posted recently is that Haskell is experiencing some growth. I have the redmonk stats: http://redmonk.com/sogrady/category/programming-languages/ and http://sogrady-media.redmonk.com/sogrady/files/2014/01/lang-rank-114-wm.png which shows that Haskell is maintaining its position. My google trend analysis shows Haskell roughly matching Scala and both of them somewhat higher than F#. I admit to being a google trend novice so caveat lector! I have this using google trends: http://www.google.com/trends/explore#q=haskell%20programming%2C%20scala%20p… Thanks in advance for any help in this. Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

1 0

hmatrix-labeled: request for comments
by Nikita Karetnikov 21 Feb '14

21 Feb '14

I like how easy it is to import data in R and Octave. (See [1] for a typical workflow.) Since I couldn’t find any matching library on Hackage, I cooked up my own [2] in a couple of days. Here’s an example. Let’s start by creating a poorly formatted dataset: $ cat > test.txt One Two Longish Four Foo 1 -2 3.0 4.0 Looooooong 5.0 6.0 -72.0 8.0 Baz 41.0 4.2324234e7 43.0 1.111111144E-12 Then we parse it with ‘readFile’, mangle the data a bit, and display in GHCi: λ> import qualified Data.Packed.LMatrix.IO as L λ> import qualified Data.Packed.LMatrix as L λ> do m <- L.readFile "test.txt"; return . L.trans . L.reverseRows $ L.map (+1) m (4><3) Baz Looooooong Foo One 42.0 6.0 2.0 Two 4.2324235e7 7.0 -1.0 Longish 44.0 -71.0 4.0 Four 1.0000000000011111 9.0 5.0 Now I’m wondering how to make it better. I’m planning to add the documentation, augment the parser to accept CSV, and maybe support other matrix libraries. What’s missing? Would you like to see it on Hackage? And if not, why? [1] http://astrostatistics.psu.edu/su09/lecturenotes/pca.html [2] https://gitorious.org/hmatrix-labeled

4 4

fromString and toString
by Ben Foppa 21 Feb '14

21 Feb '14

I know we have class IsString a where fromString :: String -> a But do we have an inverse generic function toString defined anywhere? IsString implies that the type `a` is a subset of String; if all we have is fromString, then IsString defines *supersets* of String. To me, the most logical thing would be that IsString defines bijections to String (i.e. things that are subsets *and* supersets). The reason this came up is that I'm getting pretty sick of type-juggling different string types from different libraries (String, Text, various ByteStrings), especially since I have to tweak all the functions I use if a type changes; discovering fromString was fantastic, but without toString, I can't define something like reString :: (IsString a, IsString b) => a -> b which is great to have if your putStrLn only accepts one kind of string, and you have several distinct ones floating around. Thanks, Ben

7 8

Re: [Haskell-cafe] Rewrite NetBSD kernel driver using Ajhc Haskell compiler
by Kiwamu Okabe 20 Feb '14

20 Feb '14

Hi Johnny, On Thu, Feb 20, 2014 at 5:37 PM, Johnny Billquist <bqt(a)update.uu.se> wrote: > Are you saying that you essentially avoid GC by creating a large fresh heap > every time you call something written in Haskell, and then delete the heap > when the Haskell function returns? And that the current piece of code > running in Haskell is short enough that GC never is done? No, does not delete. Pool it. See following code compiled by Ajhc. Ajhc compile Haskell code into C code. https://gist.github.com/master-q/9109334 Please note auichIntr() function that is entry point C => Haskell. https://gist.github.com/master-q/9109334#file-hsmain-c-L2051 int auichIntr(HsPtr x272) { arena_t arena; gc_t gc; gc = NULL; arena = NULL; jhc_alloc_init(&gc,&arena); jhc_hs_init(gc,arena); int x273 = ((int)fFE$__CCall_auichIntr(gc,arena,(uintptr_t)x272)); jhc_alloc_fini(gc,arena); return x273; } The code post-calls jhc_alloc_fini() that pool Haskell heap (named megablock) into free_megablocks. https://github.com/ajhc/ajhc/blob/d93468e34f4514209048d4a92b1549e079ccd3fb/… void jhc_alloc_fini(gc_t gc,arena_t arena) { -- snip -- SLIST_FOREACH(pg, &arena->monolithic_blocks, link) { SLIST_INSERT_HEAD(&free_monolithic_blocks, pg, link); } SLIST_FOREACH(mb, &arena->megablocks, next) { SLIST_INSERT_HEAD(&free_megablocks, mb, next); } if(arena->current_megablock) { SLIST_INSERT_HEAD(&free_megablocks, arena->current_megablock, next); } Also s_alloc(), Haskell heap allocator, try to get Haskell heap from the pool. If not found, it posix_memalign new megablock. https://github.com/ajhc/ajhc/blob/d93468e34f4514209048d4a92b1549e079ccd3fb/… struct s_megablock * s_new_megablock(arena_t arena) { jhc_rts_lock(); struct s_megablock *mb = SLIST_FIRST(&free_megablocks); if (mb) { SLIST_REMOVE(&free_megablocks, mb, s_megablock, next); } else { mb = malloc(sizeof(*mb)); #ifdef _JHC_JGC_LIMITED_NUM_MEGABLOCK static int count = 0; if (count >= _JHC_JGC_LIMITED_NUM_MEGABLOCK) { abort(); } mb->base = aligned_megablock + (MEGABLOCK_SIZE) * count; count++; #else mb->base = jhc_aligned_alloc(MEGABLOCK_SIZE); #endif Regards, -- Kiwamu Okabe

1 0

Text and ByteString safety (was Naming scheme for partial functions)
by Lucas Paul 20 Feb '14

20 Feb '14

I'm still a little new to Haskell. Could someone explain how Text and ByteString "push the boundaries of 'unsafe'"? On Sat, Feb 15, 2014 at 8:40 AM, Antoine Latter <aslatter(a)gmail.com> wrote: > Yeah, that's a good point.Text and Bytestring (and other similar packages) > have been pushing the boundaries of 'unsafe' and are in wide use.

2 1

Re: [Haskell-cafe] Rewrite NetBSD kernel driver using Ajhc Haskell compiler
by Kiwamu Okabe 20 Feb '14

20 Feb '14

Hi Johnny, On Wed, Feb 19, 2014 at 11:57 PM, Johnny Billquist <bqt(a)update.uu.se> wrote: > Maybe someone with more insight could explain to an idiot like me how > Haskell garbage collection is handled when running in the kernel? First, s_alloc() is Ajhc Haskell compiler's allocator, and gc_perform_gc() is GC runner. https://github.com/ajhc/ajhc/blob/6c053b940812689fe22d2dbe2b7ad835dab8a3c7/… https://github.com/ajhc/ajhc/blob/6c053b940812689fe22d2dbe2b7ad835dab8a3c7/… The s_alloc() try to find free area. But if not, it runs GC. https://github.com/ajhc/ajhc/blob/6c053b940812689fe22d2dbe2b7ad835dab8a3c7/… By the way, where from s_alloc() get a memory chunk? Now using kern_malloc(9). https://github.com/metasepi/netbsd-arafura-s1/blob/arafura-s1/metasepi/sys/… Regards, -- Kiwamu Okabe

2 3

Functor instance derived from Monad
by Frantisek Farka 20 Feb '14

20 Feb '14

Hi cafe, when reading the Functor-Applicative-Monad proposal [1] on Haskell wiki I remembered that I have seen instance similar to instance (Monad m) => Functor m where fmap f a = a >>= \x -> return $ f x with FlexibleInstances and UndecidableInstances language extensions. But I cannot remember where it was nor can I find any useful reference. Is there some library in Hackage with this and similar instances? Can you point out some leading marks to me? Thanks FF [1] http://www.haskell.org/haskellwiki/Functor-Applicative-Monad_Proposal

2 3

Re: [Haskell-cafe] How to benckmark a Word64 -> Bool?
by Charles-Pierre Astolfi 20 Feb '14

20 Feb '14

Thanks Erik! I was kind of hoping for such a benchmark. On my system, the C version is consistently twice as fast as the Haskell version. (I tried -fllvm, but it doesn't change perf) Then I added bang patterns for the argument of only012 and in the tuple (p,q) and it now has the same runtime as C. Just for fun, I tried to void writing explicit recursion and used only combinators and this Haskell code is still as competitive as C, so the real bottleneck really was the laziness in the tuple/argument. http://lpaste.net/100153 In fact, this Haskell version takes 8 sec vs 10 sec for the C version on my laptop (input: 1000000000). I tried using Data.List.Stream, I couldn't get any performance gain, probably because the code is very close to optimal. So remember kids: - Bang pattern the heck out of your code (not a silver bullet, but definitely worth trying). - Don't rely on too much IO for benchmark. - Don't be afraid of combinators even if you want performance. - Ask on haskell-cafe, chaps here are very helpful :) -- Cp On Wed, Feb 19, 2014 at 8:39 PM, Erik Rantapaa <erantapaa(a)gmail.com> wrote: > I think a lot is being obscured by the IO subsystem. > > If you print just a count of the only012 numbers I get very different > results. > > Here are the versions I compared: > > http://lpaste.net/100142 > > and on my system the C version is about 10x faster. > > > On Wednesday, February 19, 2014 12:49:36 PM UTC-6, Charles-Pierre Astolfi > wrote: > >> Switching to quotRem gave no measurable improvements. >> After switching to ByteString, the code now runs in 9 seconds, which >> outperforms my C version. But honestly, I have no idea why. >> >> New code: >> http://lpaste.net/100136 >> >> $ ghc --make -O3 303only012.hs && time ./303only012 50000000 > /dev/null >> ./303only012 50000000 > /dev/null 9.72s user 0.21s system 90% cpu 10.961 >> total >> >> @Alois, I'm not sure how criterion can help compare my code with the C >> version, since in the C version I cannot measure the exec time of only012 >> only. What did you have in mind? >> >> Thanks everyone! >> >> >> -- >> Cp >> >> >> On Wed, Feb 19, 2014 at 7:24 PM, Levent Erkok <erk...(a)gmail.com> wrote: >> >>> Also, prefer quotRem over divMod as the former is faster. See here: >>> http://stackoverflow.com/questions/339719/when-is- >>> the-difference-between-quotrem-and-divmod-useful >>> >>> >>> On Wed, Feb 19, 2014 at 10:19 AM, Gregory Collins < >>> gr...(a)gregorycollins.net> wrote: >>> >>>> >>>> On Wed, Feb 19, 2014 at 9:36 AM, Charles-Pierre Astolfi <c...(a)crans.org >>>> > wrote: >>>> >>>>> So there's a difference, but I'm not sure if it's related to my >>>>> algorithm or related to IO/RTS. >>>> >>>> >>>> Text.Printf is slower than the C version (and uses String). Use >>>> Data.ByteString.putStr instead. >>>> >>>> >>>> >>>> -- >>>> Gregory Collins <gr...(a)gregorycollins.net> >>>> >>>> _______________________________________________ >>>> Haskell-Cafe mailing list >>>> Haskel...(a)haskell.org >>>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>>> >>>> >>> >>

3 3

How to benckmark a Word64 -> Bool?
by Charles-Pierre Astolfi 19 Feb '14

19 Feb '14

Hi, I have a Word64 -> Bool function called only012 that returns True iff the digits in base 10 are 0, 1 or 2. I wand to make sure that I'm competitive with C, so I wrote the following code: Haskell version: http://lpaste.net/100129 C version: http://lpaste.net/100128 $ ghc --make -O3 303only012.hs && time ./303only012 50000000 > /dev/null ./303only012 50000000 > /dev/null 21.44s user 0.41s system 91% cpu 23.754 total $ g++ -O3 303only012.cpp -o 303cpponly012 && time ./303cpponly012 50000000 > /dev/null ./303cpponly012 50000000 > /dev/null 13.87s user 0.03s system 95% cpu 14.577 total So there's a difference, but I'm not sure if it's related to my algorithm or related to IO/RTS. The core output of only012 looks quite tight: http://lpaste.net/100130 Am I doing the IO part right, that is fast IO that is not screwing my benckmark? I'm not so sure about that since I use a convoluted way to print the boolean result in Haskell. Cheers, -- Cp

4 5

Haskell-platform release information
by Obscaenvs 19 Feb '14

19 Feb '14

I'd like a pointer to some place containing information as to why the new HP is delayed (although I have my suspicions the reason being Xcode 5), and if there is a new schedule. Why isn't there a pointer on [1]? If one can't stay on schedule, which is sometimes understandable and I guess in this case highly so, then some info as to why this is is the least damage control one could do. But maybe there is such info already, and I am just unable to find it - except for the by now rather old discussion [2]. /fredrik [1] http://www.haskell.org/platform/ [2] https://www.mail-archive.com/haskell-platform@projects.haskell.org/msg02594… -- bugthunk.net @bugthunk

3 4

[ANN] data-default-generics
by João Cristóvão 19 Feb '14

19 Feb '14

Hi, This project is a fork of the well known data-default package, since the original author does not seem to be reachable, and has not accepted a rather useful patch in the past. It mainly adds: * Regrouped everything into a single module * Added several instances, namely Either, Text, ByteString, etc * Added Generics support patch by Jonathan Fischoff, with some additional support for recursive datatypes by me, with the precious help of José Pedro Magalhães This last point means that you can easily defined a default value for a record. See: https://github.com/jcristovao/data-default-generics http://hackage.haskell.org/package/data-default-generics-0.3/candidate If this is a duplicate effort, or a better alternative exists, please let me know. If not, I will soon publish it to hackage as 'official'. Thanks, João

1 0

Rewrite NetBSD kernel driver using Ajhc Haskell compiler
by Kiwamu Okabe 19 Feb '14

19 Feb '14

Hi all, NetBSD kernel's HD Audio sound driver has interrupt handler. The interrupt handler of the demo is re-written by Haskell language using Ajhc Haskell Compiler http://ajhc.metasepi.org/. Demo movie could be found at following link. http://www.youtube.com/watch?v=XEYcR5RG5cA At the demo, run following operations. First, set breakpoint at the interrupt of finding headphone, and see Haskell function names on backtrace. Second, set breakpoint s_alloc() function, that allocate area in Haskell heap. Make sure of calling the function while anytime running kernel. Nevertheless, playing wav file does not break up. The source code is found at https://github.com/metasepi/netbsd-arafura-s1. And a picture of the architecture is also at http://www.flickr.com/photos/masterq/12616929055/. Thank's, -- Kiwamu Okabe

3 2

how to write cabal package file for executable with unit tests?
by Richard Cobbe 19 Feb '14

19 Feb '14

What's the preferred way to write a cabal configuration file for a package that contains an executable and a test suite? The only thing I've found that seems to work is to put a thin wrapper Main.hs into the executable, put all of the actual code into the library, and then have the test-suite include the library in its build-depends list. This works, but I find it mildly annoying that I have to separate the code out in this fashion -- especially since the unit tests require me to expose modules in my library that aren't really part of the library's public interface. In more detail: This is a follow-up to a thread I posted back on Feb 2; you can see it on GMane at <http://thread.gmane.org/gmane.comp.lang.haskell.cafe/109374>. The original example (tarball attached to the first message in that thread) was a package structured as a library with unit tests. After acting on Erik's suggestion to put the library and test-suite source in different directories, I was able to compile the library without the type error I originally mentioned. However, this isn't really the package structure I want. The package is actually intended to produce a standalone executable, not a library. My original example used a library for reasons that I don't honestly remember -- I think I more or less stumbled upon that structure as something that more or less worked, given the difficulty of getting Cabal, test suites, Happy, and Alex to all work together well. So I tried replacing the "Library" section of the cabal file with an "Executable" section (sample tarball attached), but then I can't get the tests to compile. If I leave sample as a build-depends for the test-suite, then "cabal configure --enable-tests" fails with Preprocessing test suite 'sample-tests' for sample-0.4... <command line>: cannot satisfy -package-id sample-0.4-inplace (use -v for more information) If I take sample out of the build-depends list for the test-suite, then "cabal configure --enable-tests" works, but "cabal build" fails: test-src/RunTests.hs:8:8: Could not find module `Parser' It is a member of the hidden package `ghc-7.6.3'. Perhaps you need to add `ghc' to the build-depends in your .cabal file. Use -v to see a list of the files searched for. Either way, "cabal configure && cabal build" works fine; it's only when I try to build the test suite that things break down. Thanks, Richard

6 8

Thank you for the donations to Haskell.org!
by Jason Dagit 18 Feb '14

18 Feb '14

On behalf of Haskell.org, we would like to thank all the generous donors we had in 2013! Just in the last week of the year, we received about half of the total donations for the year. Nearly $900! That brings the total donations for the year to $1976! Thank you very much! We are very grateful for all the donations we receive, financial and otherwise. As examples, GlobalSign graciously provides us with a free SSL certificate for use on hackage and each year community members collectively provide countless hours of time and energy towards making the Haskell community vibrant, positive, and relevant. At the moment our primary expenses are hosting for haskell.org and hackage. The donations we have received will help ensure that we continue to have adequate hosting for the ever growing hackage! Thank you and let's continue our momentum into 2014! Sincerely, The Haskell.org Committee

1 0

Yi documentation
by Mateusz Kowalczyk 18 Feb '14

18 Feb '14

Hi all, In #yi (and other Haskell-related outlets), we ofter have people who want to try Yi but struggle one way or another. It seems that a big barrier is lack of documentation. If you had tried Yi or wanted to try it and you met with difficulties due to lacking documentation, I'd like to hear about it. Perhaps you tried to get going but just couldn't figure out how to do something in your config, or perhaps you tried hacking on the source but didn't know where to get started. If you're looking for any specific guides, I'd also like to hear about it. I (and perhaps some others) can write documentation but it helps if we have specific topics to talk about rather than taking guesses in the dark. If you want to try it out, we recommend that you read the README at [1]. If you have problems that aren't related to the documentation, you should use the issue tracker[2] to report them. Thanks! [1]: https://github.com/yi-editor/yi [2]: https://github.com/yi-editor/yi/issues?state=open -- Mateusz K.

5 12

HaskellWiki account
by Andrey Chudnov 18 Feb '14

18 Feb '14

Hi, Sorry for spamming the list with such trivialities. Long story short, I'd like to get an account for HaskellWiki. Tried e-mailing "nominolo" (at the email service from Google)", but to no avail. Could anyone, please, help me with that? Thanks! /Andrey

2 1

Re: [Haskell-cafe] Yi documentation
by Mateusz Kowalczyk 18 Feb '14

18 Feb '14

On 17/02/14 23:54, David Thomas wrote: > Does this mean generally I can't run an external command with output into a > buffer (or buffer region)? > > > On Mon, Feb 17, 2014 at 2:50 PM, Mateusz Kowalczyk > <fuuzetsu(a)fuuzetsu.co.uk>wrote: > >> On 17/02/14 22:25, David Thomas wrote: >>> Vim doesn't do concurrency either, so that wouldn't be a regression. >>> >>> >> >> Yes, but it does single thread scheduling to compensate (as does emacs) >> while Yi doesn't which means implementing quickfix (and other modes) >> isn't too viable without halting the whole editor. >> >> -- >> Mateusz K. >> > You can, it will just hang the editor while it happens. An easy test is having Yi call something like ‘sleep 5; echo foo’. It should be easy to see why it's a big problem at the moment. Personally I stumbled upon it when trying to implement myself an IRC client inside of Yi but there are many use cases. Anyway, I feel that we're getting a bit off-topic here. If you're interested in helping out with implementing the concurrency stuff, we'd love to have you: pop into #yi, look around the issue tracker and maybe even post to the Yi mailing list. -- Mateusz K.

1 0

ANN: LambdaMC: demo Haskell Android app built with the ghc-android tool.
by Anthony Mulcahy 18 Feb '14

18 Feb '14

Announcing LambdaMC: a demo Haskell Android app to calculate option prices by Monte Carlo simulation built with the ghc-android tool. Based on the example app at https://github.com/neurocyte/android-haskell-activity Functionality is limited, but it may be a useful reference for anybody developing a Haskell Android app: - Android Pause / Resume functionality. - Screen Rotation support. - Background worker thread updates the UI when the calculation is complete. - Interaction between various Android UI elements and Haskell code. Google Play listing: https://play.google.com/store/apps/details?id=org.dragongate_technologies Files LambdaMC.hs : Haskell app code DgAndr.hs : Haskell wrapper for various Android library functions DgMath.hs : Haskell option pricing code LambdaMC.java : Minimal Java code to support the main Activity LicenseActivity.java : Java Activity to display license information (need to move more code to Haskell-land) Prerequisites - An Android cross-compiler built with the ghc-android tool at https://github.com/neurocyte/ghc-android - The foreign-jni package from https://github.com/neurocyte/foreign-jni - The Haskell packages base, deepseq, transformers, mtl, text, time Building ./build_workaround.sh ( to work around the -shared and -r issue described at https://github.com/neurocyte/android-haskell-activity/issues/3 ) Install sudo adb install -r bin/LambdaMC-debug.apk best regards, Anthony Mulcahy

1 1

Re: [Haskell-cafe] Protecting against main thread exit
by Roman Cheplyaka 18 Feb '14

18 Feb '14

* Albert Y. C. Lai <trebla(a)vex.net> [2014-02-17 14:10:35-0500] > On 14-02-15 04:53 PM, Roman Cheplyaka wrote: > >Of course, all guarantees are off when dealing with SIGKILL or power > >reset, but there's one other annoying exception (no pun intended) — when > >the main thread terminates, all other threads are silently shut down, > >without any chance to clean up. > > > >Why is it done that way? Why not kill them with an async exception > >instead? That would be a more uniform behavior. > > > >Are there any good ways to protect again the main thread exit? > > > >(Note that I'm talking about a library, so I can't have direct > >control over what's going on in the main thread.) > > I guess it is a rabbit hole to have GHC RTS courteously send > exceptions to all threads, and still expect certain and timely death. > > Nothing says that a thread voluntarily dies after receiving that > exception, much less when it dies. Sure. But is it a responsibility of the RTS to ensure timely death? My main use case is when the user interrupts the program with Ctrl-C. The main thread can already ignore it, and the RTS is fine with it. I'm just proposing that all threads get a chance to clean up. If timely shutdown is important, there are plenty of external tools with customizable logic that can take care of that. > It seems to me that the cleanest way is still to have the author of > main decide and implement whichever exit strategy is correct for > his/her main and for the library he/she uses. And there are enough > tools to do it tidily, too: main can get a "finally" clause, just > like everybody else. I wouldn't call that tidy. The action for which cleanup is needed can be buried deep in the call hierarchy. For example, let's say 'a' needs to cleanup after doing its job (but no-one needs to wait for a's result). 'b' spawns 'a' in a new thread, 'c' calls 'b', 'd' calls 'c' and so on. We cannot cleanup in the "finally" clause of 'b' even if 'b' is executed in the main thread, because it's okay for 'a' to run longer than 'b'. We cannot simply pass the cleanup action up the chain of calls as a return value (although even that would be rather invasive), because when SIGINT strikes — say, before 'b' returns, the cleanup handler won't be installed yet — it will only be on its way to 'main'. The simplest option seems to be to convert the chain of calls from 'b' up to 'main' to CPS (directly or by using a monad). I hope you agree that it is too much for such a simple thing as (more or less) robust cleanup. Also, this violates DRY: I have to install the handler both for the worker thread itself (in case it gets killed by an async exception), and for the main thread (in case it decides to exit for whatever reason). Moreover, I have to ensure that the cleanup doesn't happen twice because of that. Roman

1 0

ANN: Implementations of TaPL
by Kyle Marek-Spartz 17 Feb '14

17 Feb '14

Hello, I’ve been working through Types and Programming Languages, implementing each language with a figure in the book. So far I’ve done Boolean, Arith, TypedBoolean, and TypedArith. Before I get too far, I’d like some feedback on my approach, project structure, and how idiomatic the code is. Here’s the GitHub repo: https://github.com/zeckalpha/TaPL Thanks in advance! I’m aware of the OCaML implementation, and a few previous Haskell implementations, but learning by doing is important, plus there were things I didn’t like about the other implementations. -- Kyle Marek-Spartz

1 0

Problems using tasty-golden
by Jan Stolarek 17 Feb '14

17 Feb '14

Hi *, I've been trying to write a testsuite using tasty-golden and I've run into two technical problems. I'll start with some background. I'm working on singletons library that provides Template Haskell functionality. I would like to tests whether some particular TH splices compile at all and if they compile whether they produce expected output. My plan is to attempt compilation of a file with GHC. If compilation fails then the test fails. If it succeedes then output is compared with a golden file. I am directly calling goldenTest function from Test.Tasty.Golden.Internal. I wrote this function to produce the test output: compileWithGHC :: IO (Either BSL.ByteString BSL.ByteString) It runs GHC with some specified options and returns Left stderr (if compilation fails) or Right stdout (if it succeedes). This function is passed as third parameter to goldenTest (using liftIO). Then I have a comparing function: cmp :: Either BSL.ByteString BSL.ByteString -> Either BSL.ByteString BSL.ByteString -> IO (Maybe String) If it gets two Rights then it compares them. If the second param is left then the function returns Just stderr. I've run into following problems: 1. When I try to run my test I get: message threw an exception: MY_GOLDEN_FILE: hGetBufSome: illegal operation (handle is closed) I suspect that lazy IO is getting in the way but I have no idea why exactly things go wrong. 2. I had to hardcode the path to my golden file. Otherwise the file could not be found. I suspect the reason is that test are run somewhere in dist/ subdirectory whereas my golden files are located alongside my test files. What can I do to have the golden files located without giving specific subdirectories in the source code? A bonus question. I redefined vgReadFile from Test.Tasty.Golden.Internal to return Either: vgReadFileE :: FilePath -> ValueGetter r (Either BSL.ByteString BSL.ByteString) vgReadFileE path = (fmap Right . liftIO . BSL.hGetContents =<<) $ ValueGetter $ ContT $ \k -> bracket (openBinaryFile path ReadMode) hClose k The only modification is the "fmap Right .". How can I return Left if opening the file fails? Janek

2 3

[Announcement] New release of SBV: SMT Based Verification, v3.0
by Levent Erkok 17 Feb '14

17 Feb '14

Home page: http://leventerkok.github.io/sbv/ ChangeLog: http://github.com/LeventErkok/sbv/blob/master/CHANGES.md I'm happy to announce a new release of SBV, v3.0. The most important addition is support for reasoning about IEEE-74 floating point numbers, i.e., programs using the Float and Double types. See the change-log for full details. Reasoning with floating-point is a tricky task, and SMT solvers are slowly starting to provide support for true machine arithmetic as prescribed by the IEEE-754 standard. In particular, the semantics of NaN and Infinity are both properly captured, along with proper rounding. Also supported is fused-multiply-add, and square-root functions at the logic level. Currently, only Z3 (the developer version release) has official support for this logic, and the implementation in SBV builds on top of Z3's implementation. It's likely that both Z3's and SBV might have some rough edges, so any bug reports are most welcome. There's also a new example file demonstrating the floating-point arithmetic: Formally establishing that floating point addition is not associative (finding a concrete counter-example), multiplicative inverses do not necessarily exist, etc. See: http://hackage.haskell.org/package/sbv-3.0/docs/Data-SBV-Examples-Misc-Floa… Happy theorem proving! -Levent.

3 3

create a record with all record accessors
by Henning Thielemann 17 Feb '14

17 Feb '14

I have records of type (f a) where all fields are of type "a". I want to create records that contain all field getters as elements. I can do this generically: getters :: (Traversable f, Applicative f) => f (f a -> a) getters = fmap (\n x -> Fold.toList x !! n) $ MS.evalState (Trav.sequenceA (pure (MS.state $ \n -> (n, succ n)))) 0 Applicative is only needed for "pure". That is, "Pointed f" would be enough. However, (!!) is not total and not very efficient. Is there already a type class in a package with "getters" as method or something I can build an efficient "getters" from? I suspect the answer lies in one of the "lens" modules. :-)

1 0

Announce: Software Engineering for Systems Developed in Functional Languages
by Simon Thompson 16 Feb '14

16 Feb '14

The 32nd CREST Open Workshop: Software Engineering for Systems Developed in Functional Languages Date: 24th - 25th March 2014 Venue: University College London, UK Through the kind support of the EPSRC in the form of a platform grant, we have funding to support the workshops, so registration is free (but there is a charge for registering and then *not* attending, since places are limited). Registration includes lunch on both days and light refreshments. Overview: Functional programming has become a mature practical tool for software development. Large complex functional programs require many of the software engineering techniques developed for other languages and paradigms, such as testing, slicing and refactoring. Some of these techniques, originally designed for imperative languages, such as amorphous slicing and refactoring may prove highly amendable to functional styles of programming. This workshop will bring together software engineers and functional programmers to concentrate on aspects of software engineering that can be extended, adapted and augmented for application to functional programs. Confirmed Speakers David Binkley, Computer Science Department, Loyola University Maryland, USA Sebastian Danicic, Department of Computing - Goldsmiths College London, UK Kevin Hammond, School of Computer Science, at the University of St. Andrews, UK Torben Hoffmann, Erlang Solutions, Denmark Yue Jia, CREST Centre, SSE Group, Department of Computer Science, UCL, UK Raghavan Komondoor, Indian Institute of Science, India Alan Mycroft, Computer Laboratory, University of Cambridge, UK Jerry Swan, Computing Science and Mathematics, University of Stirling, UK Don Syme, Microsoft Research, Cambridge, UK Simon Thompson, School of Computing, University of Kent, UK Dimitrios Vytiniotis, MSRC PPT group, Microsoft Research, Cambridge, UK More details and registration at: http://crest.cs.ucl.ac.uk/cow/32/ Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

1 0

Wheb 0.1 released -- Graceful shutdown, Mongo plugin, blaze example and more.
by Kyle Hanson 16 Feb '14

16 Feb '14

Hello all, This is a small release, but I thought I would tell you about it. I have added some new stuff to my Haskell server framework, Wheb. For those of you (most) who don't know about Wheb, here is Wheb's description from github: > Wheb's a framework for building robust, high-concurrency web applications > simply and effectively. Its primary goal is to extend the functionality of > the base WAI library as well as provide an easy entry point into Haskell > web servers. The only prerequisite is "Learn you a Haskell" or another > introductory Haskell course. I fleshed out some more examples, rewrote some of the documentation and made some feature improvements to make it easier to build plugins. The github repo's readme now contains a small tutorial. Probably the biggest change this release is the addCleanupHook which you can use to hook in and run IO actions after server shutdown to cleanup any open resources. Wheb handles the SIGINT signal and waits for all requests to complete before shutting down. Here is the complete changelog: - Ability to read settings from a file - Add graceful shutdown and cleanup hooks. - Ability to monitor number of active connections. - Remove Data.Default - Add builder helper function - URL encoding You can find Wheb on hackage or github: - http://hackage.haskell.org/package/Wheb - https://github.com/hansonkd/Wheb-Framework In addition to these changes, I have released Wheb-Mongo which provides Auth, Sessions and document manipulation/querying for mongoDB. - http://hackage.haskell.org/package/wheb-mongo If you have any recommendations please feel free to let me know! -- Kyle Hanson

1 0

ANN: aivika-1.1 (the simulation library for DES and SD)
by David Sorokin 16 Feb '14

16 Feb '14

Hi Cafe, Aivika is a multi-paradigm simulation library with a strong emphasis on the Discrete Event Simulation (DES) in the first order and System Dynamics (SD) in the second one. A new version introduces an infinite stream of simulation data. This stream is based on the process-oriented computation of DES (this computation in its turn works on top of the event queue and uses the continuations). So, a random input of arrivals distributed exponentially can be described as such a stream in just one line of code! There is also a processor that just a function that takes an input stream and then returns a resulting stream after the processing. The processor is a Haskell arrow, which means that we can use the proc-notation in case of need, although there is a lot of predefined combinators such as that one which unites parallel processors into one processor. There are finite and infinite queues. The library collects the statistics for theses queues. We can either work with the queue directly, or create a buffer processor for the queue (with loop-back or not). There is also so called the server that provides its own processor. It suits for modeling working places. As before, the library collects the statistics too. In my personal opinion the library was powerful enough already earlier but now it can also allow the modeler to define some models using the mentioned above streams and processors directly in a very high-level Haskell code in such a way as he/she would draw the model on the diagram like those ones which are used by some visual simulation software tools. At the same time, all parts of the library are very well integrated. Actually, all them are inter-connected, where more high-level monads are just based on more low-level ones. Now the top is the mentioned above processor (the Haskell arrow). Unfortunately, the PDF document included in the package is outdated. Moreover, it doesn't cover even 10% of the features of my simulation library. But there are example models that illustrate the most important features. Also I use them for my tests. Best regards, David Sorokin [1] http://hackage.haskell.org/package/aivika [2] http://hackage.haskell.org/package/aivika-experiment [3] http://hackage.haskell.org/package/aivika-experiment-chart

1 0

C++ exception (from *.so) catchable by Haskell??
by Nick Rudnick 16 Feb '14

16 Feb '14

Dear all, after trying around a while this seems to be a good question for Haskell-cafe to me: Is somewhere a place (e.g. some Hackage package) where intercepting exceptions from C++ library code is done, so one can look *how* it is done? Generally, it is the following: 1) Injecting code that throws a an exception in C++ library code, e.g., throw runtime_error("OOOPS..."); 2) then, I tried out everything in reach (Haskell docs, Hackage interfaces to C++ considered to be well-done) to get it caught (try, catch, bracket, finally; various exception types; forkOS). 3) To my surprise, every time the output stays the same: terminate called after throwing an instance of 'std::runtime_error' what(): OOOPS... Is it possible at all to get a grip of this? Is there some place where it is done? Does the terminate call already happen with the C++ execution? Any comment welcome, cheers, Nick

5 13

GHC 7.6.3 (and others) hashes
by Alexander Solla 16 Feb '14

16 Feb '14

Hi everybody, I'm building up a body of SaltStack "states" for developing with and running Haskell web-apps. Since I am hoping my project will go big (don't we all?) I'm hoping to do things right, the first time (up to the constraints of marginal costs...) So, to that end, I'm trying to go a little overboard on the systems security front, since the costs are so low. Is there any where I can find SHA hashes for the official GHC builds? In particular, I'm looking for a hash for the file located at: https://www.haskell.org/ghc/dist/7.6.3/ghc-7.6.3-x86_64-unknown-linux.tar.b… I suppose downloading via an encrypted http connection goes a long way to mitigate MITM, etc. And I realize that long term, I'll want to host my own copy (and I will). But that is quickly sliding up the cost curve. Plus, I won't know if the copy I host will be okay unless I get the hash from a trusted source. Is there some place to get that hash? Thanks!

7 12

Protecting against main thread exit
by Roman Cheplyaka 16 Feb '14

16 Feb '14

When using forkFinally or bracket, I like to have the guarantee that the cleanup action will be executed regardless of how the action or thread is terminated — normally or via an exception. Of course, all guarantees are off when dealing with SIGKILL or power reset, but there's one other annoying exception (no pun intended) — when the main thread terminates, all other threads are silently shut down, without any chance to clean up. Why is it done that way? Why not kill them with an async exception instead? That would be a more uniform behavior. Are there any good ways to protect again the main thread exit? (Note that I'm talking about a library, so I can't have direct control over what's going on in the main thread.) Roman

1 0

[ANN] anonymous-sums
by Omari Norman 15 Feb '14

15 Feb '14

Someone once wondered why there are no anonymous sum types in Haskell: https://groups.google.com/forum/#!topic/haskell-cafe/cIxfLdcJ7aI Wonder no more: http://hackage.haskell.org/package/anonymous-sums Occasionally I have needed this so I split it off into a package. If there is already something like this out there (or some elegant way to do this that doesn't involve hairy extensions), please let me know and I will be all too happy to deprecate this. Omari

6 8

Naming scheme for partial functions
by Michael Snoyman 15 Feb '14

15 Feb '14

Greg Weber and I have been discussing some changes to mono-traversable[1]. One of the modules we provide is Data.NonNull, which provides total versions of functions like `last`. A change we're looking at would require having a partial version of `last` defined in a separate typeclass (IsSequence), which would allowing for more optimized implementations of the total `last` function for datatypes which support it (e.g., strict ByteStrings). But what should we name it? I'm sure everyone's familiar with the `unsafe` naming convention, but that's not appropriate here: standard usage shows `unsafe` meaning a function which can cause a segfault. I initially named it `partialLast`, but partial can also imply partial function application. Greg brought up the idea of suffixing the function with something like `Throws` or `Errors`, which I think I'm a bit partial to myself[2]. So my questions are: * Is there some already used naming scheme out there for partial functions which I've missed? * Do people have any ideas to throw into the mix? Michael [1] https://github.com/snoyberg/mono-traversable/pull/21 [2] Pardon the pun.

4 8

HGamer3D 0.3.0 on Github
by Peter Althainz 14 Feb '14

14 Feb '14

Dear All, HGamer3D version 0.3.0 is finalized and on Github. www.hgamer3d.org www.github.com/urs-of-the-backwoods/HGamer3D News: runs on Linux and Windows, example Games/Cuboid2.hs with FRP regards Peter Althainz

1 0

ANN: asynchronous-exceptions
by Roman Cheplyaka 13 Feb '14

13 Feb '14

It is often useful to distinguish between synchronous and asynchronous exceptions. The common idiom is to run a user-supplied computation catching any synchronous exceptions but allowing asynchronous exceptions (such as user interrupt) pass through. base 4.7 (shipped with GHC 7.8) will have SomeAsyncException type that solves this problem. asynchronous-exceptions is a new package that serves two purposes: * provide compatibility with older `base` versions that lack the `SomeAsyncException` type * define convenient functions for catching only synchronous exceptions Roman

6 21

Lisp Style Restarts in Haskell
by Christopher Howard 13 Feb '14

13 Feb '14

Hi. I was curious if Haskell has something like "restarts" in Common Lisp. My search engines didn't give relevant results for "Haskell restarts". However, there were several results for "Haskell coroutines" and, from what I can gather, restarts and coroutines are a similar or related subject. -- http://www.lugod.org/presentations/pgp/why.html

5 4

ghci in gallery
by Duncan Rowland 13 Feb '14

13 Feb '14

Dear All, new to haskell, so this might be obvious, but... I'm setting up a gallery installation (OSX) that exposes a command line haskell to the visitors. The process is run with user 'nobody', so hopefully that will be a bit safer, i.e. cat visitor_commands_pipe | sudo -u nobody ghci -XOverloadedStrings But how question are: 1) what sort of damage could a malicious user do to my system by entering commands into the pipe? 2) what should I do to protect my system? I can filter the user commands as I like, but I do not want to run 'in a webpage'. Thanks in advance, -Duncan.

4 4

ANN: generic-maybe-0.3.0.2
by Jonathan Fischoff 12 Feb '14

12 Feb '14

generic-maybe utilizes GHC.Generics to generalize the functions of Data.Maybe to arbitrary sum types with two constructors, with one "empty." Here is a quick example: λ> :set -XDeriveGeneric λ> import GHC.Generics λ> data Result a = Success a | Fail deriving (Show, Generic) λ> fromMaybe 'a' Fail 'a' λ> fromMaybe 'a' $ Success 'b' 'b' Additionally, it lets you convert between two representations: λ> convert (Just 'a') :: Result Char Success 'a' Documentation on Hackage: http://hackage.haskell.org/package/generic-maybe-0.3.0.2/docs/Data-Generics… -Jonathan Fischoff

1 0

Lazy lists with with call-by-value reduction strategy.
by flicky frans 12 Feb '14

12 Feb '14

Hello. I am currently writing lists with lazy semantics in the pure lambda-calculus with call-by-value reduction strategy. Here is an example: http://pastebin.com/SvQ5hCSD Here is a simple interpetator: http://pastebin.com/mejCWqpu Am I reinventing the wheel? Are there some sources, from where i can learn more about lazy evaluation in the strict languages?

5 7

Lazy Lambda Calculus implementation
by Chris Warburton 11 Feb '14

11 Feb '14

Hello all, I've written the following implementation of Lambda Calculus, which will evaluate its Terms non-strictly. I've verified this since the Y combinator works without diverging: data Term a = Const a | Var Nat | Lam (Term a) | Term a :@ Term a data Val a = C a | F (Partial (Val a) -> Partial (Val a)) type Env a = [Partial (Val a)] eval' :: Term a -> Env a -> Partial (Val a) eval' (Const c) env = Now (C c) eval' (Var n) env = let Just x = lookUp env n in x eval' (Lam f) env = Now (F (\a -> eval' f (a:env))) eval' (f :@ x) env = do F f' <- eval' f env Later (f' (eval' x env)) eval t = eval' [] t Nat, Partial, lookUp, etc. have pretty obvious implementations. My question is, will this behave lazily? In other words will the contents of the 'env' lists be shared between the different contexts, such that forcing an element the be evaluated twice will only perform the evaluation once? Note that the first "do" line is the only place where evaluation is forced. If anyone could point out an 'obvious' reason why it will or will not be shared, or approaches I can take to check or infer this myself (eg. a Term which would show wildly different RAM usage in each case), I'd be very interested to know. I'd also be interested if someone spots a bug ;) For those who are curious, the code is living at https://gitorious.org/lazy-lambda-calculus and I've written a blog post detailing the iteration's I've been through at http://chriswarbo.net/index.php?page=news&type=view&id=admin-s-blog%2Flazy-… Cheers, Chris

2 1

A new yaml module
by Michael Snoyman 11 Feb '14

11 Feb '14

The yaml package[1] currently provides two modules. Text.Libyaml is a lower level, streaming API which is essentially a raw exposure of the underlying libyaml C library. Data.Yaml uses the aeson Value data type and ToJSON/FromJSON type classes for higher level serialization. For many cases, this approach works well, though there are problems: * There are problems with roundtripping, since YAML allows for ambiguity about the data type of values[2]. For example, in the yaml snippet `foo: 1234`, is 1234 intended to be numeric or a string? Either is valid. * YAML is intended to be human-readable output. But Data.Yaml provides no control over the encoded representation, e.g. should we use single or double quotes for a string (or no quotes at all), or the order of values in a mapping[3]. For other examples, just look at the issue tracker for yaml[4]. I don't want to drop the current aeson-based functionality, since I think it's still valid and useful in many cases. But I do think it's worthwhile to add in an alternative API which handles YAML-specific constructs better. My idea is: * Create a new Data.Yaml.Aeson module, and have it mirror Data.Yaml. * Deprecate Data.Yaml. * Create a new Data.Yaml.? module to contain this YAML-specific API. I'm asking for feedback on that last point. I have some basic ideas on what such an API would look like, but given that there are many people using YAML in ways different than how I'm using it, I don't think an API designed entirely by me will suit all use cases. I've opened up a new issue[5] to track this work. If you're interested in participating in this design, please contact me. I'm happy to have the discussion on this mailing list, but if (as I suspect) there are just a handful of people who are interested in pushing this forward, it likely makes sense to take the discussion offlist. Michael [1] http://hackage.haskell.org/package/yaml [2] https://github.com/snoyberg/yaml/issues/22 [3] https://github.com/snoyberg/yaml/issues/37 [4] https://github.com/snoyberg/yaml/issues [5] https://github.com/snoyberg/yaml/issues/38

4 4

How Plugins works with a Cabal sandbox
by Joey 11 Feb '14

11 Feb '14

I was wondering, could somebody talk me through how the Plugins package works with a Cabal sandbox, or Cabal in general? Basically, I'm writing a program where I want to dynamically load and run user-supplied code. There are two cabal DBs in question: the sandbox which I'm using to build my program, and my "global" sandbox located in /home/user/.cabal. Which database, if either, does a program I load with System.Plugins.Load.load have access to via "import" statements? How can I avoid double-loading of packages? In particular, I'm currently getting this error when I try to load my code. Any thoughts? GHCi runtime linker: fatal error: I found a duplicate definition for symbol transformerszm0zi3zi0zi0_ControlziMonadziTransziError_mapErrorT1_closure whilst processing object file /home/joey/.cabal/lib/transformers-0.3.0.0/ghc-7.6.3/HStransformers-0.3.0.0.o This could be caused by: * Loading two different object files which export the same symbol * Specifying the same object file twice on the GHCi command line * An incorrect `package.conf' entry, causing some object to be loaded twice. GHCi cannot safely continue in this situation. Exiting now. Sorry.

1 0

Master's Thesis: Open areas of research in Haskell
by Tyler Huffman 11 Feb '14

11 Feb '14

Hello all! Beginning in September, I'll begin my Master's program in Computer Science, and I'm completely set on doing my thesis in some form of functional programming and/or Haskell. I've seen the Internship opportunities and areas of research for GHC (https://ghc.haskell.org/trac/ghc/wiki/Internships) but they all seem to apply to Ph.D candidates. That said, are there open areas of research that I could look into, or more resources in Haskell that would be useful for a two-year program's research? I'm hoping to have a set thesis by the time I begin my Master's program, which is why I'm giving myself six months in advance. Any help would be highly appreciated! Regards

2 2

Haskell meeting in Regensburg, 2014-02-11, 20:00
by Andres Löh 10 Feb '14

10 Feb '14

Hi. Tomorrow, there will be another Haskell meeting in Regensburg, Germany: Tuesday, 11 February 2014 20:00 Binary Kitchen, Walderdorffstr. 13b, 93053 Regensburg There'll be no official talk or presentation, but the theme of the session is going to be "Performance". If you have Haskell sample code that runs slower than expected, feel free to bring it along. The plan is to discuss a number of small demo problems and consider best practices for improving performance of Haskell programs. Everyone who's interested in Haskell is welcome. No actual knowledge of Haskell is expected or required. We'll speak German and/or English, depending on who's going to be there. If you'd like to get updates about future Regensburg Haskell meetings or vote on when we meet next, please join our mailing list at http://lists.binary-kitchen.de/listinfo/haskell If you have any questions and for some reason don't want to join the mailing list, you can also email me :) Cheers, Andres -- Andres Löh, Haskell Consultant Well-Typed LLP, http://www.well-typed.com

1 0

haskell-search.org | research tools for Haskell
by m＠j4.pe 09 Feb '14

09 Feb '14

Hello, I would like to introduce http://haskell-search.org/. The idea is to index the most common Haskell sites to facilitate research on Haskell. It is a version for testing. If you like it, I can leave it running. Regards

2 2

Package for regular expressions
by Daniil Frumin 09 Feb '14

09 Feb '14

Hi, everyone! Due to the recent discussions discussions about regex- packages on libraries@ and cafe, as well as due to the unicode bug in darcs that Erik Kow and I have stumbled upon I wanted to ask the Haskell community the following: What is up with the regular expression packages? Which one is the go-to package? There are really a bunch of them around (regex-compat, regex-tdfa, regex-posicx, regex-compat-tdfa,, ..) and it's not obvious at all what is the difference between them and which one should I use. Any advice or comments are appreciated. Sincerely yours, -- Daniil Frumin

5 4

Installing Ghc 7.8 - ghc-split missing
by Magnus Therning 09 Feb '14

09 Feb '14

I've put together an experimental package of Ghc 7.8 for ArchLinux. It's pulling the sources from git (the branch ghc-7.8 from git.haskell.org) and it basically performs the following steps to build and install: ./sync-all -r git://git.haskell.org get -b ghc-7.8 ./boot ./configure --prefix=/usr make -j 5 make DESTDIR=<the packaging dir> install The build and install completes successfully, and some trivial tests work (compiling hello-world, playing a bit with ghci, that sort of thing). However, compiling mtl fails, with this message: Configuring mtl-2.1.2... Building mtl-2.1.2... Preprocessing library mtl-2.1.2... [ 1 of 21] Compiling Control.Monad.Writer.Class ( Control/Monad/Writer/Class.hs, dist/build/Control/Monad/Writer/Class.o ) ghc: could not execute: /usr/lib/ghc-7.8.0.20140204/ghc-split And indeed, ghc-split is not installed using `make install`. Is this a known bug? /M -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus I invented the term Object-Oriented, and I can tell you I did not have C++ in mind. -- Alan Kay

1 0